See below link to great tips in pruning OGRs. I don't know if it applies to Austin roses in the Old Rose Hybrid group.

"I prune my repeat bloomers to stimulate growth and better, more continual blooming. The early spring pruning gets rid of thin, unproductive wood in the roses which drain energy away from flower production. The rule of thumb is that you should cut out any growth less than the diameter of a pencil."

"Scarman prunes his old roses three times a year. The first pruning is done during the dormant season and the roses are cut to what he calls pruning height. This is a little below the height you want the roses to be during the summer and it is at the height where there are enough strong canes on the outside to provide support to the more flexible inner canes. The second pruning is done just as the buds are showing color. Its aim is to remove non blooming vegetative growth. This showcases the flowers and redirects the rose's energy to produce more stems. The third pruning happens in late summer where the roses are pruned back to where they flowered and are shaped."